Patent GB-1167024-A (GB)
Title: Static Regenerative Direct Current Motor Control.
IPC: H02P7/28
Filed: 1966-10-03
Abstract: 1,167,024. Control of D.C. motors; converting. WEB PRESS ENG. Inc. 3 Oct., 1966 [21 Oct., 1965], No. 44039/66. Headings H2F and H2J. [Also in Division G3] A D.C. motor 22 is energized from a three-phase source 28 through an armature circuit comprising controlled rectifier bridge 62 adapted for regnerative operation, the field winding 26 being supplied reversibly from transformer 42 through rectifiers 44, 46, or 48, 50. Initially, a source 30 is adjusted to provide a signal, representing the desired speed, this signal being applied to operational amplifier 16 having direct and inverse output signals proportional to the input signal. A firing circuit 52 for the field rectifiers receives the inverse output signal to determine the desired direction of rotation of the motor. Both the output signals from the amplifier 16 are fed to a logic circuit 66, to determine whether conditions are proper for motoring or regenerative operation, by means of the polarity of the output signals and the field polarity signals in conductors 68, 69. Acceleration of the armature 24 causes tachometer generator 34 to provide a feedback signal which reduces the error signal in line 40. The firing circuit 64 responds to retard the firing-angle of the controlled rectifiers in bridge 62. Regenerative operation is introduced by reducing the reference signal or by an overhauling load, thus reversing the error signal and the output signals from the amplifier 16. The motor field excitation is reversed, the inductive energy stored in the field being regenerated. The correct signal in conductor 68 or 69, indicating complete field reversal, provides a signal from circuit 66 to circuit 64 for regulating the armature rectifiers in accordance with the magnitude of the error signal. The amplifier 16 becomes saturated when the error signal is excessive, and control is taken over by a current regulator. A current feedback signal is taken from the armature circuit and applied to the circuit 66 which alters the output signal to circuit 64, after comparing the feedback signal with a reference signal comprising the saturated output of the amplifier 16, to retard the firing angle of the armature rectifiers and to maintain the armature current at the desired maximum. The operational amplifier 16 comprises two complementary, three-stage transistor amplifiers, the first amplifier having a feedback control for maintaining the combined output signal at a constant value, whereby a change in the output signal of one amplifier causes an equal but opposite change in the output signal from the other amplifier, Fig. 3 (not shown). Resistors 54, 56, in the field circuit provide current-limiting if the field rectifiers misfire. The circuit 52 comprises two uni-junction transistor networks each associated with one group of controlled rectifiers and providing firing pulses through transistors. The firing circuits have a main energization circuit comprising a differential amplifier and separate circuits which provide signals slightly less than those necessary to place the uni-junction transistors in a conductive state until the end of each half-cycle is approached. Pulses are then supplied to discharge the field winding through the controlled rectifiers to the source, to reduce the field current rapidly. The circuit 52 is synchronized with the source voltage by a transistor which is associated with a Zener diode and supplies power across two base terminals of the unijunction transistors, Fig. 4 (not shown). The circuit 64 comprises three separate firing networks, each connected to a complementary pair of rectifiers in the bridge 62. The inputs to the firing networks are stabilized by current feedback each network comprising an input transistor connected to a uni-junction transistor whose output is applied to a two-transistor assembly equivalent to a four-layer semiconductor. The latter is associated with a unijunction oscillator for determining the supply of firing pulses to the armature rectifiers in synchronism with the A.C. supply frequency, Fig. 5 (not shown). The circuit 66 comprises a pair of AND-gates receiving the signals on lines 238, 68, and 239, 69, respectively. A current-regulating portion of the circuit 66 is associated with the gates and comprises transistors in a differential stage and receiving the armature-current feedback signal, Fig. 6 (not shown).